Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT
Not Applicable.
1. Field of the Invention
The present invention relates generally to agricultural implements, and, more specifically, to hydraulic systems for lifting and controlling the depth of such implements.
2. Related Art
Typical multi-frame agricultural implements, such as field cultivators and chisel plows, use a hydraulic system to vary the depth that the implement enters the earth during field-working operations and to provide adequate ground clearance during transport. Some hydraulic systems, such as shown in U.S. Pat. No. 3,663,032, employ rephasing cylinders connected in series to raise and lower the frames in unison. A flow control valve on the towing vehicle extends or retracts the series connected cylinders in unison. The cylinder capacities and strokes usually must be carefully matched for proper cylinder operation. Also, leakage across the seals of one or more cylinders causes the cylinders to get out of phase, which results in uneven operation across the width of the implement. To rephase the cylinders, the machine normally must be fully raised, which results in loss of time and operating efficiency.
Other systems rely on mechanical depth stops to control operating height, but do not allow the operator to change that height from the cab or to easily vary depth for different transport conditions, ground contours and soil conditions. In addition, both the series cylinder and the mechanical depth stop systems require mechanical adjustment outside the cab to adjust the height of wing frames relative to the main or center frame. Adequate level control for fore-and-aft frame leveling or tilt and for leveling from side to side have presented problems.
On implements with a main frame and individual wing frames, depth of penetration of the wing sections often varies from that of the main frame, but the rephasing cylinder arrangement fails to accommodate easy and reliable adjustments of the wing sections relative to the main frame. The stroke and size of the wing frame cylinder sometimes is determined by the cylinder matching requirements of the hydraulic system, rather than by lift capacity and space considerations, so that the cylinders are not optimal or most economical.
As a consequence, a system that enables the control of the individual cylinders at each wheel of the implement was developed and is described in U.S. Pat. No. 5,957,218. That system has a master selection control valve which is controlled by the operator when it is desired to raise or lower the implement. The master selection control valve meters the flow of hydraulic fluid into supply lines that extended to a plurality of three-position, four-way control valves. Each of those four-way control valves is associated with one of the cylinders and is operated independently by a solenoid in response to a signal from an implement control unit.
To raise the implement, a signal from the implement control unit causes the solenoid to move the respective control valve from the center blocking position into a position at which the base end of the associated cylinder is connected to the supply line of pressurized fluid and the rod end of the cylinder is connected to a tank return line. When it is desired to lower the implement, a signal causes the solenoid to move the valve to the opposite position to apply pressurized fluid to the rod end of the cylinder and drain fluid from the base end. By individually controlling the control valve for each cylinder, a given wheel can be independently raised or lowered, thus enabling one side of the implement to be positioned higher than the other side,
This hydraulic system is relatively expensive and complex as requiring a separate three-position, four-way control valve for each wheel of the implement.
The present invention provides a hydraulic system to control the lift and depth across the entire width of an implement.
An agricultural implement has a frame supported by a plurality of movable lift assemblies that are capable of raising and lowering the frame relative to the ground. A lift system is provided move the lift assemblies using pressurized hydraulic fluid from a supply line. Following use, the hydraulic fluid is recycled through a tank return line.
The lift system has first and second hydraulic lines which are selectively coupled to the supply and tank return lines by a primary control valve. In a preferred embodiment of the system, the primary control valve comprises a three-position, four-way valve which is controlled by the implement operator. A separate hydraulic cylinder is associated with each lift assembly to produce the mechanical force that raises and lowers the frame in a controlled manner. A lift valve circuit, comprising a plurality of two-position lift control valves, couples the plurality of hydraulic cylinders to the first hydraulic line and the second hydraulic line.
In one version of the present invention, each hydraulic cylinder has a first port connected to the second hydraulic line and has a second port. A plurality of lift control valves couples the second port of the hydraulic cylinders to the first hydraulic line to control flow of hydraulic fluid there between. Each lift control valve is controlled individually so that its associated lift assembly may be independently operated.
Operation of the primary control valve determines whether the implement is to be raised or lowered. Activation of specific ones of the plurality of lift control valves determines which sections of the frame are to move and the amount that a given section moves with respect to the other sections.
In the preferred embodiment, transducers are provided to produce electrical signals indicating the actual position of each lift assembly. A control unit compares the actual position to a desired position for each lift assembly and closes a particular lift control valve when the associated lift assembly reaches the desired position. The remaining lift assemblies continue to move until they reach their individual desired positions.